Subtract : 3a ( a + b + c ) - 2b (a - b + c ) from 4c ( -a + b + c)

Please explain the various steps.

solve it this way

3a(a+b+c) -2b(a-b+c) = 3a² + 3ab +3ac -2ab + 2b² -2bc 

 =3a² +ab + 3ac + 2b² -2bc  ....... (1)

Now evaluate the following 

 4c(-a+ b+c) = -4ac + 4bc +4c²  ....... (2)

Now subtract (1) from (2)

(-4ac + 4bc + 4c²) -(3a² +ab + 3ac + 2b² -2bc)  = - 4ac +4bc+4c² -3a² -ab -3ac -2b² +2bc 

 =(-4ac -3ac) + (4bc +2bc) +4c² -3a² -ab -2b² 

 (-4ac + 4bc + 4c²) -(3a² +ab + 3ac + 2b² -2bc) = -7ac + 6bc +4c²-3a²-ab-2b²

which is the answer.